The global positioning system (GPS) is based on an earth-orbiting constellation of twenty-four satellite vehicles each broadcasting its precise location and ranging information. In order to calculate a three-dimensional location, a receiver must determine the distance from itself to at least four satellite vehicles. This is accomplished by first determining the location of at least four satellite vehicles using ephemeris data received from the satellites. Once the locations of the satellites have been determined, estimates of the distance from the receiver to each of the satellites are calculated based upon the measured time it takes the signals to travel from each satellite to the receiver. The position, and the accurate time of measurement, of the receiver may then be determined by a method of triangulation.
Many mobile phones include an integrated GPS receiver. A GPS receiver allows a mobile service provider to determine the location of the mobile phone typically within tens of meters. This is mandated for emergency services by most governmental communication agencies. For example, providing emergency 911 (E911) services for mobile phones is mandated by the Federal Communications Commission (FCC) in the United States. In addition the current geographic location of the mobile phone can be used for a variety of other purposes, including providing walking or driving directions to a user or providing location-based information and search results to phone applications.
During manufacturing of a mobile phone, testing is performed to ensure the mobile phone is operating properly. “Fast self testing” may be employed to quickly check that all components are mounted and are operating properly. This includes both the GPS receiver circuitry and the regular cellular transceiver circuitry. External test equipment is generally employed to perform assembly testing for the GPS receiver circuitry. Such testing equipment typically includes harnesses that connect to the mobile phone components to be tested. Further, the test equipment may require routine maintenance and calibration. All of these factors contribute towards less efficient manufacturing and higher testing costs. Manufacturing costs could be reduced and efficiencies increased if testing of the GPS receiver circuitry could be accomplished without use of external testing equipment. It would be advantageous if inherent operating characteristics of the mobile phone could be used to perform testing.